In order to determine the composition of measuring mediums such as gases, gas mixtures, or fluids, very diverse analysis sensors are used in process metrology. An analysis sensor generally comprises a measuring sensor that is designed to generate a measuring signal depending upon an analysis measurand, especially one dependent upon a concentration of at least one analyte in the measuring medium, as well as measuring electronics that determine a measured value representing the analyte concentration in the measuring medium on the basis of the measuring signal. An analyte is one substance or several substances, especially solutes, that are contained in the measuring medium and whose concentration in the measuring medium is to be determined and/or monitored by means of the analysis sensor. The measuring electronics may at least partly be integrated into a measuring transducer arranged directly at the measuring point, with the former having a housing with means for display and input, e.g., a screen or input buttons or keys.
Examples of analysis sensors are conductivity sensors, especially conductive or inductive conductivity sensors, density and viscosity sensors, pH sensors, ion-selective electrodes, dissolved oxygen sensors, gas sensors, and photometric sensors that are designed to determine the concentration of a substance present in a photometric measuring path by means of a photometric absorption measurement, especially Raman spectrometers or NIR spectrometers. Analysis sensors, especially those mentioned here, may be designed as in-line measuring devices whose measuring sensor is integrated into a process receptacle in order to capture a measurand of a measuring medium contained in the process receptacle or flowing through the process receptacle. The process receptacle may, for example, be a basin, a fermenter, or a pipeline and/or a pipe system in a process plant.
It becomes obvious in some applications, where analysis sensors are used in flowing process media, that the quality of the measuring values provided by the analysis sensors frequently depends upon the flow characteristics, especially the flow rate of the measuring medium. The flow rate, especially volume or mass flow rate, is to be understood as a volume and/or a mass of a medium that moves through a cross section, especially a cross section of a process receptacle related to the period of time.
In process metrology, flow rate sensors are often used in addition to analysis sensors for process monitoring and control, which are, for example, used as flow monitors (also referred to as flow switches) or are designed as flow rate measuring devices. Flow monitors serve for qualitative flow rate capturing, especially the determination as to whether or not a medium flows through the process receptacle. Flow rate measuring devices furthermore serve to determine a flow rate measuring value for the medium flowing through the process receptacle. The flow rate sensors are usually integrated into the process receptacle as in-line devices like the analysis sensors mentioned above. They are often arranged in a wall of the process receptacle or comprise a measuring tube that can be integrated into the process receptacle. A flow rate sensor, especially of a flow monitor or a flow rate measuring device, is designed to generate a measuring signal that represents the volume flow rate or the mass flow rate of the measuring medium flowing through the process receptacle and/or the measuring tube. Usually, the measuring sensor is connected with measuring electronics that receive the measuring signals generated by the flow rate sensor and determine flow rate measuring values, in the case of a flow rate measuring device, and a qualitative signal representing the presence of a flow, in the case of a flow value. The measuring electronics may be integrated, at least partly, into a measuring transducer for flow rate sensors as well, featuring a housing with means for display and input.
Known measuring principles that are applied in flow rate sensors according to the state of the art are calorimetric or thermal methods, magnetic-inductive methods, Coriolis methods, effective pressure methods, Doppler methods, ultrasonic transit time methods, transit time methods with laser light, whirling and/or vortex methods, or mechanical methods. Please refer to “Durchfluss-Hanbuch, Ein Leitfaden für die Praxis: Messtechniken-Anwendungen-Lösungen” (Flow Rate Manual—A guide for practical use: measuring techniques—applications—solutions), Endress+Hauser Flowtec AG (eds.), 4th edition, Reinach, 2003, for an overview of those methods.
It may be necessary to determine the amount of analyte carried by a flowing measuring medium within a certain period of time, i.e., a so-called analyte load or a flow rate in relation to the flow rate in some applications for the monitoring and control of industrial processes in process plants. It is required for this purpose that the measuring values from various sensors be collated, e.g., an analysis sensor and a flow rate measuring device. In this, the measuring values captured by the measuring electronics of the various sensors must be either read or transferred to a superordinate processing unit—for example, a process control unit. Direct determination of such an analyte load or a check of the measuring value quality is directly at the measuring point, as well as the display by means of a measuring transducer arranged directly on site, is, therefore, frequently not available without complications. Superordinate processing units such as process control units are, furthermore, not always available in smaller process plants.